Rapid prototyping systems are well known. The following U.S. Pat. Nos. are believed to be representative of the state of the art: 5,545,367, 5,544,550, 5,542,070, 5,515,903, 5,491,643, 5,459,868, 5,458,825, 5,453,934, 5,448,687, 5,433,280, 5,426,722, 5,398,193, 5,386,500, 5,307,499, 5,289,214, 5,287,435, 5,263,130, 5,177,689, 5,157,423, 5,139,338, 5,031,120, 4,961,154, 3,633,113, 3,507,660, 3,411,686, 3,410,310, 3,368,989, 3,262,808, and 3,248,444.
Rapid prototyping methods of the art include stereolithography, solid ground curing, selective laser sintering, fused deposition modeling and droplet deposition, which are all discussed briefly in "Unraveling rapid prototype methods", M. K. Raymond, American Machinist, June 1996, pages 24-31.
Fused deposition modeling (FDM) is an extrusion method for thermoplastic material, developed and commercialized by Stratasys Inc., Eden Prairie, MN. In FDM, a continuous filament of a thermoplastic polymer or wax is passed through a heated nozzle. The material is delivered as a wire into an extrusion head and heated so that it is extruded at a temperature slightly above the flow point. The material solidifies rapidly after deposition, each layer being fused to the previous layer. A drawback of FDM is that external supports are generally needed to support the deposited layers. The external supports must be removed after completing the model.
U.S. Pat. No. 5,578,227 to Rabinovich describes a model making method including delivering thin, continuous feedstock of materials which have various profiles with opposite flat sides and fusing the feedstock by adhesion or welding of a flat side with an energy source to a flat side of a previous layer, while keeping the feedstock cross-section in substantially original shape. The "adhesion" of the Rabinovich method is not adhesive but rather a term used alternatively to "welding" to describe the joining of one layer to a previous layer. Rabinovich is limited to laser welding one flat side of a layer to another flat side of a previous layer, and the method cannot be used for any cross-sectional shape. Additionally, the method is limited to weldable materials.